normal feeding activity in March and August but not in May. The dormant condition is evident in juvenile H. scabra, where individuals of 4–14 cm in length
responded to changes in temperature. Specifically, the maintenance of a constant
warm temperature prevents H. scabra from burrowing (Mercier et al. 1999).
Holothuria theeli is undoubtedly a non-selective, generalist feeder throughout the
rainy and dry seasons, and appears to be a forager. It feeds at an almost constant
daily rate and probably continues to feed through stormy periods. The lowest
percentage of prey organisms (such as micro invertebrates and microphytobenthos) occurred in March and the highest in August. The major food sources of
H. theeli were crustaceans, foraminiferans, diatoms, and detritus. High levels of
meiofauna and microphytobenthos in the gut contents of H. theeli indicate that
both play a significant part in the nutrition of the holothurians without any relationship to the size frequency distribution of the sediment around holothurians
(Sonnenholzner 2003).
Sea Urchins
Eucidaris galapagensis
Distribution and Density
Although there were different expeditions since the 1800s to qualitatively study the
Galápagos marine diversity, including sea urchins, it was not until the 1950s that
information on abundances of sea urchins became available. In 1954, the slatepencil urchin Eucidaris galapagensis Döderlein, 1887 (Fig. 6.3b) occurred at a
mean density of 19 ind m
-2 in the western islands (Malmquist 1991). During the
1970s, some studies indicated that its densities around the archipelago fluctuated
between 2–8 and 34–50 ind m
-2 (Wellington 1975; Glynn et al. 1979; Glynn
1990).
Some years later, Glynn (1988) compared the densities of E. galapagensis
before and after El Niño 1982–1983 and found that they had increased from 5 to
30 ind m
-2 . He also found that E. galapagensis fed on hermatypic coral polyps
and dead corals, which were highly impacted by the warming event. This
explained the dramatic increase of the urchin abundances after El Niño (Glynn
et al. 1979; Glynn 1988). Similarly, Edgar et al. (2010) examined historical data to
document the spatial and temporal scale of recent changes in species distributions
and important benthic habitat types. Part of the study included the analysis of
underwater images (taken in 1982, 1983 and 1984) to assess changes in the
densities of E. galapagensis before and after El Niño 1982/1983. They found that
densities of this species significantly increased by a factor of about two from 1982
(0.45 ind m
-2 ) to 1984 (1.0 ind m
-2 ).
Brandt and Guarderas (2002) reported E. galapagensis was the most common
and abundant sea urchin species in the whole archipelago, with an average density
200
J. Sonnenholzner et al.
responded to changes in temperature. Specifically, the maintenance of a constant
warm temperature prevents H. scabra from burrowing (Mercier et al. 1999).
Holothuria theeli is undoubtedly a non-selective, generalist feeder throughout the
rainy and dry seasons, and appears to be a forager. It feeds at an almost constant
daily rate and probably continues to feed through stormy periods. The lowest
percentage of prey organisms (such as micro invertebrates and microphytobenthos) occurred in March and the highest in August. The major food sources of
H. theeli were crustaceans, foraminiferans, diatoms, and detritus. High levels of
meiofauna and microphytobenthos in the gut contents of H. theeli indicate that
both play a significant part in the nutrition of the holothurians without any relationship to the size frequency distribution of the sediment around holothurians
(Sonnenholzner 2003).
Sea Urchins
Eucidaris galapagensis
Distribution and Density
Although there were different expeditions since the 1800s to qualitatively study the
Galápagos marine diversity, including sea urchins, it was not until the 1950s that
information on abundances of sea urchins became available. In 1954, the slatepencil urchin Eucidaris galapagensis Döderlein, 1887 (Fig. 6.3b) occurred at a
mean density of 19 ind m
-2 in the western islands (Malmquist 1991). During the
1970s, some studies indicated that its densities around the archipelago fluctuated
between 2–8 and 34–50 ind m
-2 (Wellington 1975; Glynn et al. 1979; Glynn
1990).
Some years later, Glynn (1988) compared the densities of E. galapagensis
before and after El Niño 1982–1983 and found that they had increased from 5 to
30 ind m
-2 . He also found that E. galapagensis fed on hermatypic coral polyps
and dead corals, which were highly impacted by the warming event. This
explained the dramatic increase of the urchin abundances after El Niño (Glynn
et al. 1979; Glynn 1988). Similarly, Edgar et al. (2010) examined historical data to
document the spatial and temporal scale of recent changes in species distributions
and important benthic habitat types. Part of the study included the analysis of
underwater images (taken in 1982, 1983 and 1984) to assess changes in the
densities of E. galapagensis before and after El Niño 1982/1983. They found that
densities of this species significantly increased by a factor of about two from 1982
(0.45 ind m
-2 ) to 1984 (1.0 ind m
-2 ).
Brandt and Guarderas (2002) reported E. galapagensis was the most common
and abundant sea urchin species in the whole archipelago, with an average density
200
J. Sonnenholzner et al.